In my previous U.S. Pat. No. 4,043,191 there is taught a dynamometer apparatus for measuring the tension in a pair of spaced, elongated members, and in particular, the tension in a sucker rod string associated with a downhole pump and a pumpjack unit.
Some pumpjack units are massive in construction and reciprocate a sucker rod string which extends downhole thousands of feet to a production formation where the sucker rod string actuates a downhole pump. The cost of the entire installation, including the borehole, often amounts to more than a million dollars. The downhole pump must be sized in accordance with the production rate of the hydrocarbon-producing formation as well as being properly sized respective to the pumpjack unit. An entire field of endeavor is associated with pumpjack-actuated, downhole pumps, and there are specialists in the oilpatch whose profession is to properly select the proper pump size, pump stroke, rod size, and pumping speed in order to obtain maximum production from the underlying hydrocarbon-producing formation, while at the same time, optimum, economical operation of the equipment is achieved.
A pumpjack unit preferably reciprocates the downhole pump at a speed which maintains the hydrostatic head in the borehole at an acceptable minimum. From time to time the rate of production of the formation may change, or perhaps the speed of the pumpjack or the size of the downhole pump has been improperly selected, whereupon an undesirable condition is encountered called "pump-off".
When a deep well "pumps off", fluid pounding is incurred, and this phenomenon is detrimental to the entire pumping unit and sometimes causes damage to a pump or results in a broken rod string. This is a catastrophe in the oilpatch because an expensive pulling unit must now remove the thousands of feet of rod string so that the pump can be repaired or the rod string replaced. In other instances, the pump sometimes will be undersized, or the pump speed will be inappropriate for the optimum rate of production, all of which tends to lower the production efficiency.
It therefore would be desirable to have available a means by which the characteristics of a pumpjack unit can be monitored for an extensive length of time, with the data from the monitored well being stored so that it can be rapidly consulted at some subsequent time. An apparatus by which the above desirable measurements can be realized is the subject of the present invention.